Unsure if this is something that's changed since the comments from August 2016, but had Idol of Decay cast Dark Rebirth on me while at 262 HP. Hopefully that helps narrow down the exact threshold for the idol's Dark Rebirth cast.

this strat is really unreliable. I don't know if the tamer got a buff or these pets got a nerf but I've had my Idol die off 4x in a row now long before I could Sandstorm on the Lantern. I'm guessing there should be some more deflections in there instead of just spamming crush over and over, but they aren't noted in the strat.